Silverlight 4 (now in Beta) seems to have support for microphone&webcam. You will need to create server side for it as well. Probably some kind of user management and contact list. There will be significant bandwidth if you get lot of users, so the server side should created be scalable to multiple machines. Maybe Azure cloud ? With any platform you choose it will take lot of effort.

I belive that you did not undestand that this think you ask, if you going to build it its takes months of design and developing.

if you search for "web chat webcam" you maybe see why I say that.

For example this http://www.ivideochat.com/ site have developed a program for that reason. See how complicate it is, how many think have.

Also you did not say, what platform you using, what is your server that going to split the video channels and send them all over the other, are you going to use it for one to one, or all to all, are you going to build it on asp.net ? on linux, on flash, on what ?

Some times small thinks in words, are too huge in developing.

So for me you must define a lot of thinks and then maybe you can see if you can do that.1.Media stream server ? example http://www.adobe.com/products/flashmediaserver/2.Developing platform.3.Number of possible users.4.The way they goint o interact each other.5.All of them need to have camera ?6.What about bad users (that show bad thinks) ?7.Do they going to chat also ?

Think about all that first, then maybe is more clear to you what you going to get.

Architecturally, you need a server to relay the video/audio to both parties, since they cannot connect directly.

You need a Silverlight or Flash 'movie' running in the browser, which you have written, and you need a server to do the relaying.

Its relatively straightforward using Haxe.

Haxe is a Free language for creating both Flash 'movies' and server applications (and more; read their homepage).

One of the Haxe-related servers that is available for Free is HaxeVideo - literally a video server that (among other things) supports live streaming from clients. Run HaxeVideo on a server and you can easily make Flash clients (written in the Haxe language naturally) do video chat.